This study is intended to find out whether teacher’s feedback can improve students’ writing skill in writing hortatory exposition text or not and to know the aspect of writing which is improved more after teacher’s feedback. To gain the data, the writer conducted an experimental research in SMAN 1 Model PBKL Peukan Bada in which the writer acted as a teacher. To conduct this study, the writer used one group pretest-posttest design. The writer took one class from six classes by applying purposive sample technique and took nineteen students. Pre test was conducted before experimental action in order to know the students’ achievement before the treatment. On the other hand, post test was conducted to know the students’ achievement after the treatment. To find the differences between pre test and post test achievement, the writer used t-score. The result shows that the mean score of the pre test is 53.97 and the score of the post test is 71.03and the result of t-score is 7.68. The t-Value at the level significant 0.05 is 2.101 and at the level of significant 0.01 is 2.878 with the degree of freedom 18. Since, the result of t-test is higher than t-Value, the alternate hypothesis is accepted. In other words, there is a significant difference between pre test and post test score. It proves that the use of teacher’s feedback is effective to improve students’ achievement in writing hortatory exposition text. In addition, it was found out that the aspect of content is improved more than other aspects of writing.